Features & Benefits

Incorporates Sonardyne's 6G® Technology

Incorporates Sonardyne's Wideband 2® signal Technology

Extends performance of USBL systems

Resilient to acoustic aeration and noise

High update rate and repeatability for greater vehicle control

Vendor independent USBL aiding

IMO-certified AHRS: parallel INS output

Sparse LBL saves operational time and vessel costs

Measurement redundancy increases data integrity

Flexible installation options

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SPRINT

SPRINT (Digital Version)

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SPRINT: Subsea inertial navigation aids ROV positioning

Oceaneering ROV flies with SPRINT

SPRINT (Subsea Precision Reference Inertial Navigation Technology) is an acoustically aided inertial navigation system for subsea vehicles. The system extends the operating limits of Ultra-Short BaseLine (USBL) and can dramatically improve the operational efficiency of Long BaseLine (LBL) by using sparse arrays. SPRINT makes optimal use of acoustic aiding data from acoustic positioning and other sensors such as Doppler velocity log (DVL) and pressure sensors. This improves position accuracy, precision and integrity in any water depth while reducing operational time and vessel costs.

Acoustically Aided INS

The seamless integration of acoustics and inertial technologies exploits the long term accuracy and precision characteristics of acoustic positioning with the continuous availability and fast update rate of state-of-the-art inertial sensors. A single navigation solution is computed and output to a display with intuitive status and quality metrics.

Standard output telegrams are available for ROV and Survey company use.

The additional integrity offered by Inertial integration significantly reduces operational delays during periods of challenging subsea acoustic conditions such as aeration and noise. The precision and update rate of the output allows greater subsea vehicle control and is suitable as an ROV station keeping input.

SPRINT can be aided by USBL or LBL acoustic inputs. The USBL aiding is vendor independent when using a standard position message or can be tightly coupled to a Sonardyne Marksman or Ranger 2 to optimise performance. Alternatively, LBL aiding can be from a sparse array of one or two beacons only.

The core of the system is the Lodestar platform. Lodestar was released to the market in 2007 as a premium quality, survey grade Attitude and Heading Reference System (AHRS) for surface and subsea applications. Using the same hardware platform, Lodestar is now central to SPRINT.

Lodestar makes use of three ring laser gyroscopes that measure the angular rate and three accelerometers that measure the specific force of a moving platform. The highest quality dual use (commercial and military) field proven sensors have been selected for use due to their performance, low mean time between failure (MTBF) and ease of export. These sensors have highly stable error characteristics and are compensated for temperature variation making them ideally suited to subsea applications.

The INS sensor outputs are combined mathematically to compute the position, velocity and attitude of the vehicle. The output is extremely low noise and very accurate in the short term but slowly degrades over time. Therefore it is necessary to seamlessly aid the INS with complimentary acoustic positioning.

Acoustic Aiding

Sonardyne’s latest Sixth Generation (6G®) vessel-based transceivers and subsea transponders maximise the benefits of the system by providing the most precise and reliable acoustic aiding input. Previous generation Sonardyne transceivers and transponders are also compatible with SPRINT.

The vessel-mounted USBL transceiver determines the range and bearing to an acoustic transponder fitted to the subsea vehicle. Using vessel DGPS for position and VRU/MRU/AHRS for vessel motion compensation, an absolute position for the vehicle mounted transponder is calculated by the USBL system.

This position is fed into SPRINT as an absolute positioning aiding input. Additionally, the USBL system is synchronised to Coordinated Universal Time (UTC) to provide an accurate timestamp. Whilst the use of Sonardyne USBL ensures a tighter acoustic / inertial integration and the best possible USBL positioning performance, SPRINT can accept position aiding from any USBL system that uses correct time-stamped positions in an industry standard telegram.

Although SPRINT improves USBL system precision, it will not resolve any inherent systematic errors that are present. Users must therefore ensure that the USBL system they are using is correctly calibrated and recommended operating practices are observed, for example, using regular sound velocity profiles.

Sparse LBL

In Sparse LBL operations, one or two (instead of four or five) transponders are deployed on the seabed and their positions derived using ‘box-in’ or other top-down calibration techniques. With a known transponder position, the INS can navigate in Sparse LBL mode using the ranges from one or more seabed deployed transponder to acoustically aid the INS and constrain error growth in the absolute position output. In this configuration, the vehicle mounted LBL transceiver (RovNav 6) communications will be routed to the vessel via the Lodestar for optimal time stamping of acoustic range data.

Vehicle-Mounted Sensor Aiding

Lodestar has the ability to use vehicle-mounted aiding sensors such as Doppler velocity logs (DVL) and pressure/depth sensors. The use of these sensors provides further benefits for subsea navigation such as the ability to provide precise and continuous navigation output even if external acoustic positioning is lost for periods of time.

SPRINT does not need to be physically co-located with the Doppler Velocity Log or integrated into the same housing. Only ‘coarse’ alignments and offsets from the INS to the DVL are needed from the user. Fine offsets and misalignments are then calculated in the field using a calibration routine. This approach allows for more flexible mounting configurations to be considered.

The SPRINT processing software is installed on a Sonardyne Navigation PC which is typically located on the vessel’s bridge or in a survey room.

All sensor position and timing information is interfaced through the INS software which is easy and intuitive to use. Users can configure and control the system whilst logging all inertial navigation data for analysis or post processing. Various displays allow performance of the system to be assessed, including real-time inertial quality indicators, inertial external position comparison and system health.

The Lodestar INS unit installed on the subsea vehicle is interfaced to the topside using a single serial or Ethernet connection through the vehicle’s umbilical. The powerful Kalman filter and proven inertial navigation algorithms are processed subsea ensuring that Lodestar retains inertial navigation and attitude measurement capability even if there is a loss or unreliability of communications.

The unit is depth rated up to 5,000 metres and has a battery backup that can sustain operations for up to two hours if external power is lost. This ensures SPRINT can maintain its inertial and AHRS algorithms, eliminating the need for re-initialisation before navigation can resume when power is restored.

SPRINT is time synchronised to Coordinated Universal Time (UTC) by receiving time updates from the topside INS software. It can also receive 1PPS timing pulses from the vessel DGPS and for optimal time synchronisation this configuration is recommended.

Post Processing

Sonardyne’s INS post-processing software package complements SPRINT. It provides Kalman smoothing of Lodestar IMU and aiding sensor data for improved navigation accuracy and integrity. The software provides the ability replicate real-time results offline and to repair issues experienced in real-time, such as the use of an incorrect offset. Also included, is the control and screening of aiding sensor data use and settings including offsets and mounting angles. Similarly, sensor aiding and Kalman filter settings can be controlled. Navigation data can be exported in selected text formats.

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